Thermal plasma is generally used for disposal of wastes, development of new material, elimination of noxious gases, etc.
The core technology in thermal plasma relates to plasma torch generating ultra high temperature of plasma. Among the plasma torches, DC (direct current) arc plasma torch of hollow type is most widely used.
The plasma torch of hollow type has electrode generating DC arc inside. The electrode has a particularly designed inner space of which the front side and the rear side have a front electrode 2 and a rear electrode 3, respectively, to confine ultra high temperature of plasma that is conductive fluid and to give necessary properties. The inner space is connected to the electric discharge electrode of the torch nozzle and serves as guide to finally discharge the plasma focused on a fluid arc spot to the outside.
Particularly, the electrode and electrode nozzle of the plasma torch are made of OPC (oxygen free copper) material for easy arc ignition.
However, since the front electrode and electrode nozzle of OPC material are places on which DC arc spot is focused, they are fast eroded due to high temperature of arc heat.
Still in the case of torch of reverse polarity type, the erosion in the cathode spot is larger than in the anode spot.
And in a melting furnace system using the plasma torch, the torch electric discharge electrode of OPC material is inserted into the melting furnace for operation and thus is exposed to high temperature of plasma atmosphere.
Therefore water cooling is necessarily required to lower the rate of erosion in the front part of the torch and this deteriorates heat efficiency of the plasma torch.
Also a behavior of plasma in the melting furnace is less reproducible and always has large uncertainty. The torch nozzle exposed to this situation is easily damaged in the cooling channel even by small side arcing.
In this case, the operation is stopped and the nozzle must be replaced with new one. This will lower the efficiency of operation.
Further, since the price of OPC is expensive and the nozzle is also very expensive because of difficult processing process of it, it is generally uneconomical.
The electrode nozzle of OPC material in conventional plasma torch is very expensive in its price and causes side arcing. Thus it has problems of short life cycle, low operating efficiency and economical infeasibility.